BROOKITE

TiO₂
Orthorhombic

Brookite, a titanium oxide mineral, was first reported from Franklin by Gordon (1951, reprinted in 1976); it has not been found at Sterling Hill.

Description

Gordon described rare, black, stout, prismatic crystals, less than 2 mm in size and elongate on [100] (Figure 22-45).

	Figure 22-45. Crystal drawing of brookite from Franklin. Drawing from Gordon (1951).		Figure 22-46. Prismatic highly-modified crystal of brookite from the Buckwheat Dolomite at Franklin. Field of view is 1.5 mm in maximum dimension.

More common, yet still rare, are the brookite crystals with the habit shown in figure 22-46. Additionally, as illustrated by Peters et al. (1983), Franklin brookite may be tabular (Figure 22-47), bladed, or equant in habit.

	Figure 22-47. Tabular pseudohexagonal brookite crystal from the Buckwheat Dolomite. Field of view is 0.2 mm in maximum dimension. Photograph courtesy of Tom Peters and the Paterson Museum.

Crystal faces are commonly tarnished and may have discernible coatings. Local brookite is reddish-brown, dark brown, yellow, or black, with indistinct cleavages and adamantine luster on freshly broken surfaces. Broken crystals are recognized by the high luster and matrix. Within the Buckwheat Dolomite only rutile, sphalerite, and anatase have as high a luster, and they have different habits. Brookite is differentiated from sphalerite by the distinct cleavages of the latter. There are no analytical data for local specimens. 

Occurrence and paragenesis

Franklin brookite is found in vugs in the Buckwheat Dolomite, associated with rutile and a large number of other species, as described by Peters et al. (1983). Brookite is also found in the Kittatinny Limestone.